30 



DYNAMICAL GEOLOGY. 



inner curve by deposit, and the winding tends ever to 

 become greater and greater. This is most conspicuous 

 in cases in which rivers run between mud-banks made by 

 their own deposit. In such cases, thecmjpves. bejQipjne 

 greater and greater, until finally two contiguous curves 

 cut into each other, the river straightens^itself, and the 

 old bend is thrown out and becomes a lagoon (d, Fig 9). 



FIG. 9 a, b, c, successive stages in the winding course of a river. 



Many such lagoons exist in all rivers which run through 

 swamp-lands. Fig. 9 shows the process, and Fig. 10 is a 

 portion of the lower Mississippi River showing the result. 



FIG. 10. A portion of lower Mississippi. 



^ 3. Flood-Plains and Their Deposits. 



Rivers usually rise in hilly or mountainous regions, and 

 flow in the lower course through flat plains. In flood 

 seasons, the velocity being checked by change of slope, 

 the channels are 110 longer able to contain their waters, 

 which therefore overflow portions of the flat lands on each 

 side. The area liable to overflow is called the flood-plain. 

 In case of great rivers draining interior continental basins, 

 the flood-plains are very large. The flood-plain of the 



